On the reaction Si+(2P) + H2(X1Σ+g) → SiH+ + H. I. Ab initio potential energy surfaces

An ab initio unrestricted Hartree-Fock investigation on the C_∞v (1²Σ⁺, 1²Π) and C_2v (1²A₁, 1²B₁, 1²B₂) potential energy surfaces of the Si⁺ (²P) + H₂ system is presented. In the study, the MIDI-1* minimal gaussian basis set of Huzinaga and co-workers is used. The analysis of the stationary points and main features of the potential energy surfaces involved and the comparison with those of the isovalent C⁺ (²P) + H₂ → CH⁺ + H reaction reported in the literature have allowed us to understand the different dynamical behaviour exhibited by both isovalent systems near their respective threshold energies.     

Rotational dependence of the proton-transfer reaction HBr+ + CO2 → HOCO+ + Br. II. Comparison of HBr+ (2Π(3/2)) and HBr+ (2Π(1/2))

The effects of reactant ion rotational excitation on the exothermic proton-transfer reactions of HBr(+)((2)Π(1/2)) and DBr(+)((2)Π(1/2)), respectively, with CO(2) were studied in a guided ion beam apparatus. Cross sections are presented for collision energies in the center of mass system E(c.m.) in the range of 0.23 to 1.90 eV. The HBr(+)/DBr(+) ions were prepared in a state-selective manner by resonance enhanced multiphoton ionization. The mean rotational energy was varied from 3.4 to 46.8 meV for HBr(+)((2)Π(1/2)) and from 1.8 to 40.9 meV for DBr(+)((2)Π(1/2)). Both reactions studied are inhibited by collision energy, as expected for exothermic reactions. For all collision energies considered, the cross section decreases with increasing rotational energy of the ion, but the degree of the rotational dependence differs depending on the collision energy. For E(c.m.) = 0.31 eV, the cross sections of the deuteron transfer are significantly larger than those of the proton transfer. For higher E(c.m.) they differ very little. The current results for the exothermic proton transfer are systematically compared to previously published data for the endothermic proton transfer starting from HBr(+)((2)Π(3/2)) [L. Paetow et al., J. Chem. Phys. 132, 174305 (2010)]. Additional new data regarding the latter reaction are presented to further confirm the conclusions. The dependences on rotational excitation found cannot be explained by the corresponding change in the total energy of the system. For both the endothermic and the exothermic reaction, the cross section is maximized for the smallest rotational energy, at least well above the threshold.     

THE EXPRESSION OF ENTEROTOXIN A~-B~+ GENE OF V. cholerae IN E. coli

The cloning in E. coli of a cholerae toxin gene that is A~-B~+ has been successfully constructed by using DNA recombinant techniques. E. coli cells carrying the recombinant plasmid pMM-CTB have been shown to produce a large amount of CTB subunits which are secreted as extracellular proteins.     

电子转移反应O~2+O~2^.^-→O~2^.^-+O~2的从头算研究

利用abinitio方法,在UHF,UMP2及不同基组3-21G,6-31G^*,6-311+G^*和UMP2(full)/6-311+G^*水平上,研究了O~2/O~2^.^-自交换电子转移反应。优化了电子转移前后反应物和产物的结构,研究了体系能量的变化,计算了自交换电子转移反应的内重组能。对UHF方法和UMP2方法的计算结果进行了比较,并与实验结果进行了对照。结果表明UHF方法由于没有考虑组态相互作用,计算结果存在较大偏差,UMP2(full)/6-311+G^*水平上的计算结果与实验值吻合较好。在UMP2(full)/6-311+G^*水平上计算了气相自交换电子转移反应速率常数。在优化了电子转移复合物结构的基础上考虑了溶剂效应的影响,计算了水溶液中的溶剂重组能。研究结果表明O~2/O~2^.^-体系电子转移反应的活化能主要来源于溶剂重组能的贡献。最后计算了该反应在水溶液中的反应速率常数。理论计算结果与实验值吻合得很好。     

盐酸在氨基酸水溶液中热力学性质的研究 I. 甘氨酸+盐酸+水体系

Standard potentials (E°_m) of the Ag-AgCl electrode in Glycine+H_2O mixture at 25 ℃, 30 ℃, 35 ℃, 40 ℃, and 45 ℃ have been determined from the EMF measurements of cells of the type: Pt, H (g, 101.325 kPa)|HCl(m)+Glycine+H_2O|AgCl-AgThese values have been utilized to evaluate the transfer energetics (ΔG°_t, ΔH°_t, ΔS°_t) accompanying the transfer of 1 mol HCl from the standard state in water to the standard state in Glycine+H_2O mixtures. Attempts have been made to explain the transfer energetics varying with different compositions of Glycine+H_2O mixtures in the light of ion-solvent interactions and the structureal effects of the solvents.     

The 2-Methoxyethanol + 1,2-Dimethoxyethane + Water Ternary System. Static Relative Permittivities from −10 To +80°C

Static relative permittivities of the 2-methoxyethanol + 1,2-dimethoxyethane + water ternary solvent system were measured as a function of temperature (-10 = t/°C = 80) and of composition, over the whole molar fractions range 0 = x₂, x₂, x₃ = 1. The experimental values have been used to test some empirical relationships accounting for the dependence of e on T, x_i, and on T, x_i couples of values. A comparison between calculated and experimental data shows that these relationships can be profitably employed to predict e values in correspondence to experimental data gaps. The excess dielectric permittivity, e^E, assumes, in the most cases, negative values for any compositions of the mixtures, while the values of the excess molar polarization, P^E, are positive. The large values of the excess quantities are indicative of the strong specific interactions among similar, as well as different molecules in the mixtures. Discussion of the data in terms of Kirkwood correlation factor also gives information on the short-range intermolecular interactions among the components, suggesting the formation of two-components adducts rather than of than more complex moieties involving all three molecular species.     

Quantum study of electronically non-adiabatic collinear reactions. III. Influence of vibrational and electronic excitations on the Cs + HH → CsH + H reaction

A new hyperspherical close-coupling method, involving non-orthogonal diabatic electronic bases adapted to each arrangement, is developed to compute collisional transition probabilities for the collinear Cs + HH system, close to the threshold of the reactions Cs^*(7p) + HH(υ = 0) → CsH(υ = 0) + H. A simple model, taking into account the overall rotation of the linear CsHH complex, provides estimates of inelastic and reactive cross sections. A hyperspherical adiabatic analysis, based on adiabatic electronic potential energy surfaces, points out two prominent features in the dynamics of the CsHH system namely: (i) Approximate electrovibrational adiabaticity, which gives rise to large cross sections (≈ 5 Ų), for both the vibrationally adiabatic process Cs^*(7p) + HH(υ = 0) → CsH(υ = 0) + H and the vibrational-into-electronic energy conversion Cs(6s) + HH(υ = 6) → CsH(υ = 0) + H. (ii) Sharp resonances, which yield rapid oscillations on total cross sections, related to the rotational structure of an intermediate linear long-lived complex.